He hasn't posted a photo since. In the past, he's typically posted a photo every two to three days.

So, what's up? Why did he slow down?

We didn't get a chance to ask Systrom about his photo abstinence at the Crunchies. A Facebook spokesperson suggested nothing was amiss, telling us that Systrom has been otherwise active on Instagram—for example, by liking and commenting on photos.

Since that's a boring explanation, we're left to come up with one on our own. Here are a few theories about why Systrom has been so silent:

Systrom may just want to understand what the Instagram experience is like for users who only view photos.Pinterest CEO Ben Silbermann did something similar, when he deleted his account and started over to get a feel for what using the service was like for brand-new users.

Could Systrom be secretly testing something new—something he can't share publicly with the world yet? That would be exciting, obviously. His photo blackout came right as Twitter was prepping and launching Vine, a service for sharing short video clips which some are saying could be the next Instagram.